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10 COMMISSIONING
1. To measure the slope, connect current signals to the relay as shown in the figure below:
= 1.5 × CT and I
2. If I
1
2
3. The slope is calculated from the values of I
I
differential
%slope
=
------------------------- -
I
restraint
4. Slowly increase I
. As I
2
minimum pickup.
5. As I
continues to increase, the element operates again when both the initial slope and the minimum
2
pickup conditions are satisfied. Calculate the initial slope 1 value at this point.
6. As I
increases further, the element may reset again, depending on the setting of the slope kneepoint. This
2
is caused by the current values moving into the slope 2 region.
7. Continue increasing I
2
g) SLOPE KNEEPOINT
1. To measure the approximate location of the kneepoint, follow the procedure above, setting I
equal to the kneepoint. Gradually increase I
The value thus obtained should be equal to the initial slope setting. Increase I
again. Calculate the slope at this point – it should be equal to the final slope. If the kneepoint is much differ-
ent than the selected value of I
2. For an accurate measurement of the kneepoint, select a value of I
3. Increase I
until the element resets. Calculate the slope – the value should be equal to the initial slope
2
value.
4. Increase I
by a small amount, say 10%, and adjust I
1
slope. Repeat until the slope value equals the final slope. The kneepoint value is the value of the restraint
current at which the slope changed in value.
Keep in mind the effects of auto-configuration on the magnitude of the current signal fed to
the differential elements when conducting the slope kneepoint test.
NOTE
GE Power Management
Figure 10–6: CURRENT SIGNAL CONNECTIONS
= 0, the element is operated as all the current appears as a differential current.
differential
×
100%
is increased, the element will reset when the differential current drops below the
2
until the element operates again. Compute the slope 2 value at this point.
until the element resets. Calculate the first slope at this point.
2
, the two values of slope will be the same.
1
745 Transformer Management Relay
10.6 PROTECTION SCHEMES
and I
as shown below:
restraint
2
just above the kneepoint value.
1
until a new operating point is obtained. Calculate the
2
at a value
1
until the element operates
10-17
10
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